1. Field of the Invention
The present invention relates to an implantable defibrillator having a large surfaced electrode in the form of a netting, a spiral, or a fabric of electronically conductive material,or having an intracardinal electrode in the form of a coil of electronically conductive material, as well as a method of producing such a defibrillator.
2. Description of Related Art
The purpose of defibrillators is to detect and treat abnormal heart rates, i.e. disturbances in rhythm and arrhythmias (see, for instance, EP-OS 0 475 027). The detection of disturbances of rhythm is effected, for instance, via myocardial screw electrodes. They detect a ventricular flutter or fibrillation by, for instance, measuring the heart rate or by recording an electrocardiogram (ECG). Upon the recognition of ventricular fluttering or fibrillation an electric shock is given off after a few seconds. The current pulse is impressed on the heart by large surfaced electrodes (patches) and/or by intracardial electrodes (see, for instance, German OS 39 14 662).
As the mechanism of action of the electric defibrillation there is assumed a synchronous irritation of all non-refractory myocardial regions. It is therefore necessary for the entire myocardial symplast to be excited simultaneously. This, however, presupposes sufficient current density.
The electrodes of defibrillators must be flexible so that they can adapt themselves to the physiological conditions of the body and the heart. Furthermore, they must be biocompatible and their surface should not irritate the surrounding tissue by additional rubbing. Resistance to corrosion, low polarization, and long-term stability are further important criteria which must be satisfied by such electrodes.
Up to now, large surfaced electrodes for defibrillators have consisted of metal nettings or spirals which are embedded on one side into a layer of silicone rubber and are contacted on the other side. While the nettings, in general, consist of titanium, the spirals consist of platinum. Between the electrically conductive netting or spiral and the surrounding tissue there is direct contact, which--due to the roughness of the metal--can lead to rubbing of the tissue. Intracardial electrodes can consists of non-metallic, electrically conductive fibers.